The present invention relates generally to a welded crankshaft having a number of individual elements and having cavities in the region of the main bearing journals and crank journals.
European Patent Document No. EP 0 090 013 B1 describes an assembled crankshaft whose individual elements each comprise a crank web having tubular segments shaped onto both sides. The individual elements are welded to one another in the region of the main bearing journals and crank journals, yielding a crankshaft whose crank journals and main bearing journals contain cavities in their interiors. This results in a considerable weight reduction compared to conventional crankshafts. In order to lubricate the bearings, oil lines that are constituted by inserted tubular lines which terminate via orifices on the outer peripheries of the journals, and are connected to one another via passages in the interior of the crankshaft, are provided in the cavities of the crank journals and main bearing journals. These oil lines make possible a directed oil flow with minimum oil volume, which provides sufficient lubrication of the bearing regions. This carries the risk, however, that the inserted tubular lines may detach during operation and damage the bearings. In addition, this type of oil guidance system via inserted small tubes is very complex to manufacture and assemble.
European Patent Document No. EP 0 090 013 B1 also describes a crankshaft in which the crank journals and main bearing journals are joined to one another by an oblique orifice. The result of this, however, is to make the cavities smaller, since additional material through which these orifices are guided must be provided in the interior of the individual elements. This diminishes the weight saving achieved by way of the cavities.
German Patent Document No. DE 195 36 349 C1 describes a friction-welded crankshaft that also has cavities in the interiors of the main bearing journals and crank journals. In this case delivery of lubricating oil along the shaft is accomplished via additional cavities that are configured in the journal region partially as annular spaces, and that are connected to one another via oil passages. A directed and effective oil flow in the regions of the bearings can thereby be ensured. However, the oil flows around the friction-welded seams in the region of the annular spaces, so that residual particles can be entrained into the oil circulation system. In addition, the wall thicknesses are kept relatively thin in configuring the double cavities, which results in a low geometrical moment of inertia for the weld surface, and accordingly in a weaker join between the individual elements.
It is an object of the present invention to provide an assembled crankshaft that is hollow in the journal region, while maintaining simplicity of manufacture, in such a way that on the one hand weld surfaces with a large geometrical moment of inertia are created between the individual elements, and on the other hand a directed oil flow for lubricating the bearings is ensured, without bringing the oil into contact with welding burr. At the same time, the lowest possible weight is to be achieved.
The present invention provides a welded crankshaft including a number of individual elements which each include a crank web having tubular segments shaped onto both sides, and are welded to one another in such a way that the tubular segments of adjacent individual elements together form main bearing journals and crank journals which respectively contain weight-reducing cavities in their interiors, the main bearing journals and crank journals each partially overlapping one another radially. The crankshaft is furthermore equipped with oil passages which include axial orifices that run substantially in the axial direction of the crankshaft, and which furthermore include radial orifices that connect the axial orifices to the journal surfaces. The oil passages (10), with the exception of the outlet openings of the radial orifices (12,13), lie completely in the overlap region (15) of the main bearing journals and crank journals (6,7), and the walls of the tubular journals (6,7) are of cavity-free configuration aside from the oil passages (10).
According to the present invention, the oil passages are implemented by orifices that run substantially in the axial direction in the overlap region between the main bearing journals and crank journals, and that transition via a radial orifice directly into the journal surface. Very little manufacturing and assembly effort is required for this, and the oil passages are free of contaminating welding burrs. The tubular journals are moreover of solid configuration, i.e., have no cavities aside from the oil orifice, so that the weld surfaces between the individual elements are particularly large and the strength and weight of the crankshaft are optimized. The weight-reducing cavities, however, can be configured at optimum size.
According to the present invention, the radial oil supply lines are located on the centrifugally inner side, overcoming the prejudice that oil delivery along the centrifugal force vector is necessary for proper lubrication. This aspect of the present invention stands in contrast to the crankshafts described in German Patent Document No. DE 195 36 349 C1 and European Patent Document No. EP 0 090 013 B1, whose oil supply lines each terminate on the centrifugally outer side of the crank journals.